"The figure they came up with is a surprise to us," he said, noting that the FAA has launched an evaluation of screw and bolt manufacturers.

A 1990 law, the Fastener Quality Act, requires that screws, bolts and other fasteners used in aircraft meet strict specifications.

In an effort to check fastener quality, investigators from the inspector general's office randomly collected 176 fasteners from the inventories of airlines and repair stations. The items were selected from a list of critical parts used in Boeing, Pratt & Whitney, General Electric and Bombardier products.

These parts were sent to the Science and Engineering Laboratory at Hill Air Force Base for testing, and 48 screws and bolts--27%--were found without correct thread dimensions, the report said.

When the Federal Aviation Administration was advised of this finding, it had the items retested by the manufacturers. When this was done by the manufacturers, only 3% were found not to comply, the report said.

"The data from the lab used in the study and the data from the manufacturers' tests have some very wide differences . . . and we are working with the IG to reconcile those differences," Brenner said.

The inspector general's report said the differences raise serious questions about quality.

Criticizing the FAA for not responding quickly, the report said that after two meetings with FAA officials the regulators launched an evaluation of screw manufacturers.

The report said that the agency needs to investigate thoroughly reasons for the difference in the two test results and should make sure manufacturers maintain quality controls.

Brenner said the FAA agreed with the suggestion to increase reviews of manufacturing quality and said it will place special emphasis on making sure manufacturers comply with FAA-approved designs.